Oct 17 (Reuters) - Pfizer Inc said on Monday it plans to begin shipping its biosimilar version of Johnson & Johnson's blockbuster rheumatoid arthritis drug Remicade in late November at a 15 percent discount to current wholesale prices.

The Pfizer drug, to be sold under the name Inflectra, is already available in Europe and other overseas markets and would be the second biosimilar available in the United States.

As it is not possible to produce exact copies of biotech drugs made from living cells, the cheaper versions are referred to as biosimilars rather than generics. They are intended to provide less expensive alternatives to pricey biologic medicines.

Remicade is J&J's biggest selling drug with U.S. sales of about $5 billion a year.

J&J's forecasts for 2016 had assumed no competition from a Remicade biosimilar this year. Its shares slipped about half a percent to $118.49 in after hours trading.

J&J was not immediately available to comment.

Pfizer said its pricing for the drug below Remicade wholesale costs does not take into account discounts to health insurers, distributors or other purchasing organizations.

In addition to rheumatoid arthritis Inflectra, like Remicade, is also approved to treat Crohn's disease, ulcerative colitis, psoriasis, psoriatic arthritis and the spine condition ankylosing spondylitits.

(Reporting by Bill Berkrot and Ransdell Pierson; Editing by Sandra Maler)